.strftime('%s') is locale-aware

gistfile1.py

from pytz import timezone
from datetime import datetime

# From http://en.wikipedia.org/wiki/Eastern_Time_Zone
# "Places that use Eastern Standard Time (EST) when observing standard time (autumn/winter)
# are 5 hours behind Coordinated Universal Time (UTC−05:00)."
us = timezone('US/Eastern')

# GMT during the winter is exactly UTC if I'm not mistaken
uk = timezone('Europe/London')

us_time = datetime.now(us)
uk_time = datetime.now(uk)

us_timestamp = int(us_time.strftime('%s'))
uk_timestamp = int(uk_time.strftime('%s'))

diff = (us_timestamp - uk_timestamp) / 60 / 60
print diff    ##  -5